Concrete abrading with free abrasive machine and method



Aug. 4, 1970 B. J. SUNDBERG CONCRETE ABRADING WITH FREE ABRASIVE MACHINE AND METHOD Filed Aug. 14, 1967 2 Sheets-Sheet 1 FIE a INVENTOR. 8549774 I .5 041084-126 lrrokmrys Aug. 4, 1970 B. J. SUNDBERG' 3,522,679

CONCRETE ABRADING WITH FREE ABRASIVE MACHINE AND METHOD Filed Aug. 14, 1967 2 Sheets-Sheet 2 FIEIE m. 4% Q I w \y v 25 25 62 45 J 451'NVENI'OR.

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United States Patent Oifice US. Cl. 51-317 6 Claims ABSTRACT OF THE DISCLOSURE This disclosure presents a method of abrading surfaces, and in particular, concrete, terrazzo, or similar surfaces. The abrading, as disclosed, comprises the use of a loose abrasive (discrete particles) spread onto the surface, and then worked against the surface with suitable abrading pads to remove films, paint, or bonded material from the surface. In addition, machines utilizing a disc with a plurality of steel pads rotating in a plane parallel to the surface being abraded for working the abrasive across the surface are disclosed. The method teaches the depositing of the free abrasive on the surface to be abraded, then moving a powered rubbing pad over the surface to work the abrasive upon the surface and remove the coatings from the surface. In one form the abrasive can be spread as uniformly as possible over the surface and a single abrading member machine is used. When a self-propelled machine having counter rotating abrading members is used, the abrasive is deposited in a small windrow between the abrading members.

BACKGROUND OF THE INVENTION Field of the invention The present invention deals in the art of mechanically abrading surfaces using loose granules asan abrading medium and using a rubbing member for rubbing the abrasive on the surface without the use of any flooding liquids such as water or detergents to aid in the abrasion.

Description of the prior art up job. To remove a coating from concrete floors, in particular, sandblasting and of course sanding machines have been used. 7

However, the sanding machines are very expensive to Operate because the abrasive on the machine is worn out very quickly when concrete is abraded into. It is desirable when you are re-surfacing concrete to actually remove a portion of the concrete itself as well as the prior coating to get a satisfactory bond for a new coating. As soon as conventional sanding machines start working on concrete, the abrasive on the paper dulls (the single exposed edge or point Wears down) almost immediately. The paper will also load up with the old coating during use. Also, the present process eliminates the need for chemical etching of concrete floors. With previous stripping processes the etching was necessary to remove surface imperfections and laitance for improved bonding of the coating.

In removing urethane coatings, in particular, and other abrasive resistant coatings, the use of sandblasting has been advanced. A number of problems arise including the tremendous amount of dust and debris that is present when sandblasting is done, and also if there are spots on the floor which have a relatively thick coating of the 3,522,679 Patented Aug. 4, 1970 urethane in relation to other portions of the floor, these spots will not abrade away as quickly as the rest of the coating. If the sandblasting is concentrated on these spots, the concrete surface around the spot will be abraded away so that it almost has a moat like depression around the portion of the floor where the urethane was thickest. This is very unsatisfactory because it gives an uneven surface to the floor and makes it diflicult to recoat without extensive repatching. When floors such as terrazzo are being finished or abraded, they usually utilize a water or some other liquid for flooding the surface. The present device uses only a dry abrasive with no flooding being necessary, although in one form, solvents are used to break down heavy coatings. When flooding of the surface is done, the drying time is a significant delaying factor.

The process makes it economical and even low cost to remove abrasive resistant coatings from concrete, wood, plastic or similar floors. It is easily employed and the amount of dust is kept to a minimum. Not only that, the method and the machine gives a relatively smooth floor surface which can be merely swept up or vacuumed cleaned after the abrading has ceased and it will then be ready for re-surfacing or the sweeping or dust retrieval means can be built into the machine.

SUMMARY OF THE INVENTION The invention herein relates to a method of abrading surfaces, such as concrete, using a loose abrasive on the surface and a rubbing pad moving over the abrasive, with the abrasive between the pad and the surface. Further, it relates to machines using the rubbing pads.

The present invention uses a small amount of abrasive in relation to the surface being covered and therefore is economical to use. The abrasive in loose form is cheap as opposed to coated (paper backed) abrasives. The loose abrasive operates efficiently and quickly. Further, it can be used on materials to which a solvent has been applied, and will break up the material from the surface while the solvent is drying, leaving a residue of abrasive particles and dried coating that can be merely swept or vacuumed cleaned from the flooring before resurfacing.

A loose abrasive will get into and clean low spots in the surface as well as high spots. Using the loose abrasive saves time because there is no changing of paper backed abrasives during operation and, of course, is less expensive to use. Each of the individual abrasive particles have a plurality of sharp edges and points that aid in the abrading, thus making more efiicient use of the abrasive qualities of the particles than coated or paper backed abrasives, which present only one or two usable points or edges for abrading and which quickly dull.

The method is adaptable to a wide degree of surface hardness by the use of different pressures on the rubbing pads and also different size and hardness of the abrasives.

The rubbing pads for working the abrasive are placed on powered rotary discs that rotate about an upright axis. The pads could be on orbital or .reciprocating members as well. A modified form of the machine shows means for varying the pressure of the rubbing pads against the surface during operation.

It is therefore an object of the present invention to present a method for using a loose abrasive for removing materials from floor or other surfaces.

It is a further object of the present invention to present a machine which will make maximum use of the abrasive in treating the floor surface.

In the drawings,

FIG. 1 is a plan view of a floor showing abrasive thereon with a machine rubbing the abrasive against the surface to remove material therefrom in accordance with the method of the present invention;

FIG. 2 is a sectional view taken as on line 2-2 in FIG. 1;

FIG. 3 is a bottom plan view of a disc used with the machine in FIG. 2;

FIG. 4 is a sectional view taken as on line 4-4 in FIG. 3;

FIG. 5 is a part schematic showing of a self-propelled machine used to practice the method of the present invention; and

FIG. 6 is a sectional view taken as on line 66 in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and numerals of reference thereon, there is shown in FIG. 1 a surface 10 which is a concrete floor or similar hard surface floor. The surface 10 has a coating which is to be removed for re-surfacing.

Shown schematically at 11 are particles of a loose granular or discrete particle abrasive spread onto the surface 10 in random manner but as uniformly as possible. After the abrasive has been spread onto the surface 10, a machine 12 is used for rubbing the grit into the surface to abrade the surface to remove any coating on the surface. As shown, the machine is a rotary disc type machine normally used for maintaining floors but comprising a substantially different rubbing disc. As shown, partially schematically, the machine includes a frame 13 mounted on rear rollers or wheels 14 and having a control handle 15. The handle 15 is used for guiding the machine across the floor. It is propelled by the action of the disc and is usually swung from side to side as it moves forwardly.

The frame mounts an electric motor 16 driven from a source of power through a conventional cord. The motor 16 has a power shaft 17 extending downwardly. A guide bearing 18 to hold shaft 17 can be used if desired. The power shaft is drivably mounted as at 19 into a hub 20 that in turn is drivably attached to a disc-like member 23. The disc member is mounted within an interior chamber 24 defined by the frame 13. As perhaps can be best seen in FIGS. 3 and 4, the disc 23 has, as shown, three rubbing pads 25, attached to the bottom surface thereof. The rubbing pads are, as shown, a steel material suitably fastened to the disc 23 with screws or other mounting members. The side edge surfaces of the pads 25 are slightly curved as shown and have leading points 26 rotationally leading the main part of the pad and tapering rearwardly in spiral fashion around the axis 27 of the disc. The pads extend all the way out to the periphery of the disc and when the disc is rotated in direction as indicated by the arrow 28, the pads will tend to force material that they engage in toward the center of the disc at the same time rubbing it upon the floor surface. This means that as the pad engages the abrasive, the abrasive will be rubbed by the pads as part of the abrasive passes under the pad and any free abrasive will be moved by the pad inwardly toward the center of rotation of the disc where the particles will be engaged by other pads as the disc rotates and the machine is moved forwardly across the floor.

An annular duct 31 formed in the housing of the ma chine surrounds the chamber 24, as shown perhaps best in FIG. 2, and this duct opens into a passageway 32 that leads into the inlet 33 of a vacuum blower 34. The vacuum blower is powdered through a separate electric motor 35 from suitable power source and has an outlet 36 leading into a filter bag 37 to separate any dust in the air from the air discharged from the vacuum blower.

The annular duct 31 surrounds the disc and any dust raised by the action of the disc will be drawn upwardly in direction as indicated by the arrows 38 through the duct 31 and passageway 32 into the vacuum blower and out through the filter bag where the solids will be separated from the air. This minimizes the dust that is raised during the loose abrading process and therefore makes the job much cleaner.

In order to change the pressure of the pads 25 on the surface being abraded, weights illustrated schematically at 39 can be placed on top of the frame 13. This will increase the pressure to the desired level.

Referring specifically to FIGS. 5 and 6, a modified mechanism for using the abrasive pads is shown. The machine is shown schematically in FIG. 5 and comprises a self-propelled floor maintenance machine, for example, the model L machine made by G. H. Tennant Company, Minneapolis, Minn. In this machine, normally a rotary floor maintenance implement is used. In this particular case, however, the mounting for the rotary implement is used for placing two arms 45, and pivotally mounting them as at 46 to the frame of the machine. The machine is self-propelled and contains a self-contained power unit and drive train. The arms 45 are controlled about their pivots 46 through the use of a hydraulic cylinder 47 acting through a conventional valve shown schematically at 48 controlling flow from a pump 49. The machine is illustrated generally at 44. The outer ends of the arms 45 are attached as at 52 to a framework 53. The framework 53 can be of any desired configuration and is used to support a hydraulic motor 54. The hydraulic motor is controlled by conventional controls from the pump 49 and in turn drives a pinion gear 55. The pinion gear 55 drives a gear 57 that is drivably mounted on a shaft 56 mounted in suitable hearings on the framework. Gear 58 meshes with a second gear 59 that is drivably mounted on a second upright shaft 57 that is also mounted in suitable bearings (not shown) on the framework. The shafts 56 and 57 in turn extend downwardly and drive spider members 60 and 61, respectively through universal joint drives. The universal joints permit the spider t0 flex to follow irregularities without moving the driving shafts. As shown, the spider members 60 and 61 have three legs and each of the legs is used to mount a steel pad 62 corresponding to the pads 25 in the previous embodiment. It can be seen that the spider members move in planes parallel to the surface being worked and that the pads, as shown in dotted lines in FIG. 6 are angled so that the abrasive material on the floor will be moved in toward the center of rotation of the spiders. The spiders are counter-rotating, as shown by the arrows.

The force with which the pads 62 engage the surface over which the machine is traveling can be changed by the adjusting of the pressure in cylinder 47. It can be seen that the cylinder is mounted as at 50 to the frame of the floor maintenance machine as well as to the arms 45. The use of a self-propelled machine, such as the machine shown at 44, permits a higher speed operation While still utilizing the principles of the method of a loose abrasive applied onto the surface being abraded and the use of abrading pads or members to work this loose abrasive onto the surface. With this machine however, a hopper can be provided and the abrasive particles deposited in one spot between the spiders. The spiders Will uniformly spread the abrasive as they rotate.

The machine also has a vacuum and filter system to remove dust raised by the abrading. The vacuum and filter system is part of the machine.

A powered cylindrical brush 65 is rotatably mounted about a transverse axis on suitable support arms 66 and is rotated in a suitable manner with power means, for example, a hydraulic motor 69. The brush rotates in a direction indicated by arrow 67 and sweeps the debris into a debris receptacle or pan 68. The machine thus does a complete operation in one pass and leaves the floor ready to recoat. The brush and debris receptacle are shown only schematically as the brush itself and means for driving it, as well as dust receptacles are well known in the art, but new in a machine combination using dry abrasive where abrading pads precede the sweeping brush as the machine moves over the surface.

As an example of actual operation, on a floor area comprising a concrete base with several coats of poly urethane floor coating, an abrasive comprising crystal quartz sand between and #40 National Bureau of Standards sieve size was spread onto the floor at a rate of approximately ten to fifteen pounds per 100 square feet. A machine such as that shown in'FIG. l was utilized "with a-rufibbing pressure approximately ten pounds per square inch on the pads. After passing'over the floor so the abrasive was worked into the surface thoroughly by 't he pads, the floor surf-ace was exposed-and all of the polyurethane was removed. Theonly cleaning-up left'to do was sweep the floor before resurfacing.

The cleaning brush can be part of the abrading machine for a one pass complete generation.

In another test, a quick drying varnish remover (polyurethane solvent) was applied to a polyurethane coating on a concrete base. The surface was wetted with solvent or varnish remover, and the same size loose abrasive was applied at the same rate as before after applying the varnish remover. The machine was run over the area while the varnish remover was still wet, and the abrasive was worked into the polyurethane coating on the concrete. Action of the combination of the varnish remover and the crystal quartz abrasive stripped the area clean in a short while. The varnish remover or solvent dried rapidly by the abrading action of the machine. The solvent speededup the removal of the urethane coatings. The surfacewas left clean and dry and merely had to be swept before .recoating. The drying of the solvent was accelerated by the abrading action. The machine moves over the floor and the residue left dried while the abrasive was being worked against and into the surface.

The use of three pads on each of the discs or abrading wheels supported by universal joints permits the pads to follow the slight undulations in a floor so that these depressions will be abraded evenly and much better than with a coated abrasive drum.

The usual range of particle size is smaller than standard screen size with a range from to #200 N.B.S. sieve size (Tyler Standard is substantially the same). The preferred size on concrete is approximately #35 to sieve size. If the particles are larger than this, the particles will tend to roll when encountered by the abrading pads and will not be ground into the surface to cut through the coating. If the particles get extremely small they are not aggressive enough to cut the coatings.

The use of this method is primarily on concrete floors. These floors are hard, somewhat irregular, and a very aggressive abrasive is needed. Such an abrasive is crystal quartz sand. Other particles, such as carborundum, silicon carbide, aluminum oxide, garnet, silica, or other abrasive particles can be used. To accomplish the action necessary in carrying out this method, the abrasive must be harder than the surface being abraded.

In summary, broadly the method disclosed for removing a surface coating from a concrete floor comprises the steps of applying an abrasive material uniformly over the surface, mechanically working the abrasive material upon the surface, and removing the residue from the surface. Additional factors include the fact that no detergents or water requiring substantial drying time are used in the abrading process. The mechanical working of the abrasive material is done with a powered member operating a plurality of abrading pads moving in a plane parallel to the "surface being abraded and also a vacuum duct surrounds the rotary member and removes dust raised thereby. The residue can also be removedwith vacuum or by a powered brush on the machine assembly. The abrasive used ranges from about #25 N. B.S. sieve size (which has an opening of .707 mm. or 0.278 in. square) to #200 N.B.S. sieve size (opening of .074 mm. or .0029 in. square) of crystal quartz applied at a rate of ten to fifteen pounds per 100 square feet. The preferred range of particle size is from #35 N.B.S. sieve size (which has an opening of .500 mm. or .0197 in. square) to #40 N.B.S. sieve size (which has an opening of .420 mm. or

.0165 in. square) applied at a rate of substantially ten to fifteen pounds per square feet of surface, and wherein the mechanical abrading is done at a rubbing pressure of approximately ten pounds per square inch on the abrading members. The preferred particles are those which pass through the #35 sieve and stay on top of the #40 screen. The size can go 'down to those that stay on top of a #200 screen.

Where the coating comprises material that can be broken down :bysolvent action, to facilitate more rapid removal a .solvent can be applied to the coating. The abrasive is worked into the coating on the surface until substantially all of the coating has been removed from the surface and the solvent has dried. Then the resultant debris is removed from the surface.

The amount of abrading done depends also on the coating that is being removed. Some coatings do not penetrate the surface to which they are applied and the base doesmot have to be abraded] very much before recoating. Other material embedded into the surface and a thin layergof the fioor material has to be abraded away before recoating. Doing this type of abrading using the self-propelled machine shown in FIGS. 5 and 6, an area of approximately 2400 square feet can be abraded in an hour. The? abrading members were rotating at 200 r.p.m.

The use of flooding liquids, such as water, requires a substantial delay between the abrading and recoating. The water has to dry before recoating. Also, there comes a question of how dry is dry. Many floors which have been wetted have been recoated before they are thoroughly dry. The new coating does not adhere properly and the floor has to be completely redone. With the present process this long drying time is avoided. Also there is no guess work as to whether the floor is dry or not. The solvents (when they are used) dry almost immediately and the old coating material is then swept up. Recoating can commence at once. This is important in business traffic lanes and other places in heavy use.

It is obvious that the size, configuration, number, material, degree of hardness and many other factors involved in the selection of rubbing pads will produce varying results. Thus, while steel is used as illustrative of the materials that can be employed, the invention is not limited to steel pads used in combination with the abrasive.

Finishing terrazzo is also easily done with the present method without use of slurrys.

Another application is to remove the upper coating of fines in newly finished concrete (the coating here is actually a layer of fines or impurities raised to the surface during final troweling). By grinding off this coating of fines a strong material is exposed. It is also porous to enhance the mechanical bond of any subsequent coatings. If desired, the grinding of new concrete can be used to eliminate the final troweling. After floating the concrete is allowed to cure and then the top coating of the concreteis removed with the present method. If curing compounds are used on the concrete these also can be removedwith the present method.

What is claimed is: 1. The" method of removing a coating of material from a concrete floor, wherein said coating comprises material that can be broken down by solvent action, including the steps of: applying a solvent to the coating,

applying a loose abrasive material uniformly over the surface,

mechanically abrading the loose abrasive against the coating using an abrading machine having a rotary disc rotating about an axis substantially perpendicular to the surface, said disc comprising a plurality of steel pads,

working the abrasive into the coating On the surface until substantially all of the coating has been removed from the surface, and the solvent has dried, and

removing the abrasive particles and residue from the surface.

2. The method of claim 1 wherein the abrasive ranges in size between #25 and #200 National Bureau of Standard sieve size.

3. The method of claim 1 wherein the abrasive comprises crystal quartz sand applied to the surface at a rate of substantially ten tofifteen pounds per one hundred square feet.

4. The method of claim 1 wherein the abrasive comprises crystal quartz sand having a preferred screen size range from #35 to #40 National Bureau of Standard sieve size applied at a rate of substantially ten to fifteen pounds per one hundred square feet, and therein the mechanical abrading is done at a rubbing pressure of approximately ten pounds per square inch on the abrading member.

5. The method of claim 1, including removing the residue by sweeping the surface.

6. The method of claim 1 wherein the abrasive comprises particles smaller than #25 National Bureau of Standard sieve size.

References Cited UNITED STATES PATENTS JAMES L. JONES, 1a., Primary Examiner US. Cl. X.R. 51-292, 177 p 

